10. Stellar Nurseries

Stars are born inside great clouds of cool gas and dust. Such a
cloud may contain thousands of denser lumps of gas; some of these
lumps collapse under their own weight. This gravitational compression
heats the gas until thermonuclear reactions can occur. When the
production of nuclear energy matches the rate at which energy escapes
into space, the collapse halts and a main-sequence star is born.

Topics:

Molecular clouds

Gravitational contraction

Protostars

Main-sequence stars

Star clusters

Reading:

Ch. 9

PROTOSTARS AND PRE-MAIN-SEQUENCE
STARS (p. 182)

Ch. 9-1

Stars
condense from clouds of gas and dust

Ch. 9-2

Supernova
explosions in cold, dark nebulae trigger the birth of stars

Ch. 9-3

When a
protostar ceases to accumulate mass, it becomes a pre-main-sequence
star

Ch. 9-4

The
evolutionary track of a pre-main-sequence star depends on its
mass

Orbital motion of stars in a small cluster. Color indicates
stellar mass; red is low-mass, blue is high-mass. Notice that the
high-mass stars tend to collect in the center of the cluster,
while smaller stars are pushed to the fringes or even ejected.